Final Year Project Presentation

1
Final Year Project Presentation

• Solar Powered Battery Charging System
• Catherine Conaghan

2
Objective

• To develop a small scale solar powered system
  that will power a DC load, which incorporates
  power management techniques, DC-DC conversion and
  a user interface.

3
Solar Power

• Renewable energy source
• Non-polluting
• Reliable
• Can work anywhere sun is shining
• No major mechanical parts
• Relatively no maintenance
• Noise Free
• Last decades

4
Project Overview
Load
DC-DC Converter
Solar Panel
Back-up Battery
Controller
5
Solar Panel

• Silicon cells combined in series or parallel
• Converts solar energy into electricity
• Cell Technologies
• Copper Indium Selenide (CIS) and Amorphous
• Monocrystalline and Polycrystalline
• Current varies with cell size and light intensity

6
Solar Panel Equivalent Circuit

Rs
Ip
Id
Rp
Vo
Iph
D
7
10 Watt Solar Panel

• Voc 22.9 V
• Isc 0.77 A

• Peak Power of 10 Watts
• Vmpp 15.6 V
• Impp 0.64 A

Shell ST10
The solar panel was tested with different
resistances under a constant light source

V
-
8
Solar Panel I-V Characteristic
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Solar Panel P-V Characteristic
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Maximum Power Point TrackingAlgorithms

• Two MPPT algorithms were considered
• Incremental Conductance Method
• By comparing incremental conductance with
  instantaneous conductance.
• Perturb Observe Method
• By periodically perturbing the PV array voltage
  and comparing the output power with that of the
  previous cycle. The operating point oscillates
  around the MPP since the system is continuously
  perturbed.

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Perturb Observe Algorithm
Start

• Algorithm was implemented using LabVIEW
• Solar panel read via a NI-USB 6009
• The voltage was measured across a high power
  resistor to read current
• Duty cycle output on NI USB 6009 digital output
  line

Set Duty Out
Read V, I
P_new VI
Duty Duty(-)
P_new gt P_old
P_old ? P_new
Duty Duty()
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LabVIEW

• Used to implement PO algorithm
• G programming
• Also used to generate a user interface through
  the front panel
• Waveforms showing voltage and current of solar
  panel
• Numeric indicator showing power
• Duty cycle displayed
• Stop button to end program

13
NI-USB 6009

• Data acquisition tool
• Read data in, and generate digital signals out
• Does not have a hardware counter, cannot generate
  digital outputs at high frequencies
• Solution M series

14
DC-DC Converter

• DC-DC converter needed for two reasons
• To implement the MPPT algorithm
• To bring the DC voltage to an acceptable level to
  power the load
• Buck converter was chosen and designed

15
Buck Converter Parameters

• The most important components are the inductor
  and capacitor
• Use Vo DVi to deduce ideal duty cycle range
  (0.3 0.5)
• Using both of these values for D, and the ?I
  equation two values for the inductor were
  calculated (2.8 mH 1.6 mH)
• Using the ?V equation the capacitor value was
  determined (21.3 µF)

16
Buck Converter Circuit
2.2 mH

LOAD

D
22 uF
Vin
-
-
PWM
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Back Up Battery

• Solar panels only generate power when there sun
  available
• Storage element is recommended
• Various rechargeable battery cell chemistries
• Lead Acid
• Nickel-Cadmium
• Nickel-Metal-Hydride
• Lithium Ion

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Lithium Ion Back Up Battery

• Up to 99 efficiencies
• Highest weight to energy ratio
• Average voltage of one Li-ion cell is 3.6-3.7
  Volts
• A Li-ion battery pack with a capacity of 4 AH
  would be enough to store all energy generated on
  the longest day of the year at maximum power
• Safety issues

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Li-ion Safety Concerns

• Overvoltage
• Over discharging can cause short circuit
• Battery packs usually include protective circuit
• Limits input voltage
• Limits discharge voltage
• Li-ion charger IC is recommended to implement
  charging profile

20
Mobile Phone Charging

• Initially it was thought a mobile phone charging
  algorithm would have to implemented
• Research showed that the charging algorithm is
  employed on the phone
• To prove this, a commercial Nokia car cigarette
  lighter charger was disassembled
• A ma34063a DC-DC converter was found
• To charge a mobile an appropriate constant
  voltage is needed, along with some circuitry
  protection

21
Summary

• Solar cell equivalent circuit, characteristics
  and various cell technologies
• Maximum power point tracking techniques
• LabVIEW G programming and user interface
• DC-DC converter design including choosing
  appropriate components and simulation in Pspice
• Rechargeable Batteries